1. Field of the Invention
The present invention relates to a device for removing rust on motor vehicle wheel brakes.
2. Description of the Related Art
In most cases, electric and hybrid vehicles are braked by a generator in order to be able to recover energy from the braking operation. On the other hand, the wheel brakes of a hydraulic brake system are used rather rarely. This may cause rust to be deposited on the brake disks of the wheel brakes, which reduces the braking power.
To improve the braking power in wet conditions, the so-called brake disk wiping is known to be carried out. In this case, the brake shoes are applied to the brake disks with light pressure, so that a water film present on the brake disk is removed. The condition “wet” is normally detected with the aid of a rain sensor. When this function is carried out, rust is also in principle removed from the brake disk. However, the brake disk wiping function for removing rust is only of limited suitability, since rust may also form on the brake disks when it does not rain for an extended time.
An object of the present invention is therefore to provide a device for removing rust on the brake disks of a vehicle.
According to the present invention, a braking device having a rust removal function is proposed which includes a control unit which automatically activates a wheel brake if at least one vehicle parameter satisfies a particular predefined activation condition. In contrast to environmental parameters, such as “wetness,” for example, all parameters affecting the vehicle itself are understood to be vehicle parameters in this case. Vehicle parameters according to the present invention are, for example: the vehicle speed, the engine torque of a vehicle engine, an ignition cycle counter content, time information such as, for example, information concerning the operating time of the vehicle, or a brake pressure. If at least one of the vehicle parameters satisfies a particular predefined activation condition, the rust removal function according to the present invention is performed by applying the brake shoes to the brake disks with a light brake pressure. This simply polishes away the rust present on the brake disk. This invention is in particular advantageous for electric and hybrid vehicles, since the hydraulic wheel brakes are used less often in these vehicles.
According to one preferred specific embodiment of the present invention, the engine torque of a vehicle engine is increased during the rust removal in order to compensate at least partially for the braking effect of the rust removal. The engine torque of the vehicle engine may, for example, be adjusted by the control unit. If the braking effect of the wheel brakes is completely compensated, the rust removal operation is no longer noticeable for the driver.
According to one exemplary embodiment of the present invention, one of the vehicle parameters is an ignition cycle counter content, which may be determined, for example, with the aid of a counter. In this case the associated activation condition is, for example, satisfied if the presently ascertained counter content is greater than the one in the most recently performed rust removal. In order to avoid unnecessary stresses of the brakes and save energy, the rust removal operation should preferably be activated no oftener than once per ignition cycle. The rust removal function may be adjusted in such a way that it is carried out only once each second, third or nth ignition cycle.
One of the vehicle parameters may also be a vehicle speed, which may be measured, for example, with the aid of wheel speed sensors. In this case, the associated activation condition is, for example, satisfied if the measured vehicle speed is higher than a determined threshold value. The threshold value may amount to, for example, 50 km/hr or it may also be lower, in the case of heavy vehicles, for example, 30 km/hr. This has the advantage that starting from a certain driving speed, the rust removal is no longer audible for the driver due to wind and tire noises.
One of the vehicle parameters may also be an engine torque of a vehicle engine, which is provided, for example, by an engine control unit. In this case, the associated activation condition is satisfied, for example, if the presently ascertained engine torque is lower than a predefined threshold value such as, for example, 80% of a maximum engine torque. This activation condition is intended to ensure that sufficient power reserves are available to be able to compensate for the braking torque by increasing the engine torque.
One of the vehicle parameters may also be a brake pressure, which may be measured, for example, with the aid of a pressure sensor. In this case, the associated activation condition is satisfied, for example, if the measured brake pressure is equal to or lower than a predefined threshold value such as, for example, 0 bar. This activation condition ensures that the rust removal function is not carried out during a brake pedal operation. An operation of the service brake could optionally also be detected using a brake pedal sensor such as, for example, a displacement sensor.
Another vehicle parameter may also be time information, which may be measured, for example, with the aid of a timer. The time information may relate to, for example, the operating time or the shutdown time of the vehicle. In this case, the associated activation condition is, for example, satisfied if the measured time duration is greater than a predefined threshold value. The rust removal function may thus be carried out, for example, every 10 or 20 operating hours.
The brake pressure exerted by the rust removal function advantageously amounts to more than 5 bar and in particular more than 10 bar. The brake pressure during rust removal is preferably higher than in the case of brake disk wiping.
The duration of the rust removal is preferably individually adjustable.